Synthesis and structure elucidation of 25,26,27,28-tetramethylcalix[4]arene tetraketone using 1D and 2D NMR spectroscopies

The 1H and 13C NMR spectra of the new calix[4]arene-based tetraketone were completely assigned by one- and two-dimensional homo- and heteronuclear experiments (1H–1H COSY, 1H–13C HMQC, and HMBC) at 400 and 100 MHz, respectively, at 25 °C standard pulse sequence. 1H and 13C spectra were measured at room temperature for 25,26,27,28-tetramethylcalix[4]arene tetraketone (1). 13C{1H}, DEPT and NMR techniques were used to distinguish the methyl, methylene and methine carbon resonance signals of calix[4]arene 1. Correlation of 1D (1H, 13C{1H}, DEPT) and 2D (HMQC and HMBC) NMR data was used to completely assign various overlapping and broad signals of calix[4]arene 1. Heteronuclear multibond correlation (HMBC) studies were used to completely assign various carbon resonances. Our results show that the conformation of calix[4]arene 1 in the solution is very similar to the cone conformation reported in the literature.